In the art of computing, differential signaling is often used to transmit data. Typically, two complementary signals are sent on two separate wires such that when one signal transitions from low to high, the other signal transitions from high to low. Differential signaling tends to provide greater immunity to noise, and reduces detection issues caused by variations in common mode components.
Several standards used in the art of computing specify differential signaling. For example, the Peripheral Component Interconnect Express (PCIe) standard transmits data via lanes. A lane comprises a transmit and receive pair of differential lines. Accordingly, each lane is composed of four wires, with data traveling in one direction upon each set of differential wires. The PCIe standard specifies AC coupling at the input circuit, with a high-pass filter allowing high-frequency components to pass to a receiver, while filtering out low frequency components. Often the high-pass filter is implemented by coupling capacitors. PCIe version 1.0a specifies a data rate of 2.5 Gbps with a maximum fundamental clock frequency of 1.25 GHz, PCIe version 2.0 specifies a data rate of 5 Gbps with a maximum fundamental clock frequency of 2.5 GHz, and PCIe version 3.0 specifies a data rate of 8 Gbps with a maximum fundamental clock frequency of 4 GHz.
Another standard used in the art of computing is the Intel® QuickPath Interconnect (QPI) standard. QPI interconnects are typically used to couple processors to each other and to other chipset components, such as I/O hubs. Like the PCIe standard, QPI specifies data lanes, with each lane comprising four wires, and with data flowing in a single direction on each set of differential wires. However, in contrast to the PCIe standard, QPI specifies DC coupling at the input circuit. QPI interconnects operate as fast as 6.4 Gbps, so a QPI interconnect may transmit data with fundamental clock frequency components from 0 Hz to 3.2 GHz. Often a single computer system will employ both PCIe and QPI interconnects.